1. Field of the Invention
The present invention relates to a process for efficiently hydrolyzing fats and oils to produce aliphatic acids. In particular, the present invention relates to a process for efficiently hydrolyzing fats and oils without the reduction of enzyme activity caused by an increase in the number of treatments. In the description, the term of "fats and oils" may mean an inclusion of a fat, an oil, a lard, a grease, and so on.
2. Description of the Background
As continuous processes for hydrolyzing fats and oils by an enzyme, there are processes wherein an lipolytic enzyme (lipase) is immobilized onto resin or membrane and used in a circulating reactor such as a batch stirring multi-stage reactor, a packed column or a membrane reactor and an oily substrate and a water-soluble substrate are circulated in countercurrent or cocurrent (JP-A 61-85195, JP-A 63-59896 and JP-A 1-98494). In any methods, however, apparatuses are complicated and the method of operating an enzyme column is very difficult.
As reaction examples in a batch circulating system, e.g. the following techniques are known: (1) a method of conducting a mixture having fats and oils mixed with water in an amount of about 60 weight % relative to the fats and oils to pass through an enzyme-packed reactor; (2) a method of conducting only fats and oils not containing an aqueous phase substrate to pass through a lipase immobilized on polysaccharide gel containing a large amount of water (JP-A 58-146284); (3) a method of mixing fats and oils with water uniformly by circulating them through a fat- and oil-storing tank and a humidifying apparatus and then conducting the mixture with the water content kept constant to pass through an enzyme-packed reactor (JP-A 4-335881); and (4) a method of introducing fats, oils, and water to a substrate-circulating chamber, feeding the oil phase substrate only to an enzyme column while the oil phase is separated from the aqueous phase, and returning the discharged reaction solution to the bottom of the substrate-circulating chamber (Kosugi, Y., Tomizuka, N., J. Am. Oil. Chem. Soc. 72;1329 (1995)).
In the process for hydrolyzing fats and oils by an enzyme, it is desired that the enzyme is not lost while attaining a sufficient reaction rate in easy operation in simple facilities and also that an oil phase product and an aqueous phase product can be separated from each other without centrifugation or a membrane.
Further, the above-described method (1) has the problem that because the enzyme is removed with time, the enzyme activity is lowered as the number of treatments is increased, although the degree of hydrolysis is high due to a high water content in the mixture. In the method (2) unlike the method (1), the enzyme is not removed with time, but water being necessary for hydrolysis tends to be insufficient while glycerol is accumulated in the immobilized enzyme, thus shifting the equilibrium to the side of fats and oils, which may result in inadequate decomposition of fats and oils. In the method (3), separation of the oil phase from the aqueous phase after decomposition (or hydrolysis) is difficult thus making a separation step and facilities therefor necessary and incidental. Further, any method of the methods (1) to (3) suffers from the problem that the apparatuses are complicated or the enzyme-packed reactor is very difficult to operate. In the method (4), the water content in the oil phase passing through the enzyme reactor is low and the separation of the oil phase from the aqueous phase after decomposition (or hydrolysis) is easy, but there is the problem that it is difficult to obtain high degrees of decomposition due to inadequate extraction of glycerol from the reaction solution.